Skip to content

Data Structures in Ergo#

In Ergo, several key data structures are employed to support its blockchain and smart contract functionality. These data structures are designed to ensure efficient and secure access to data, guaranteeing optimal performance and data integrity.

Here's a list of the main data structures used within the Ergo ecosystem:

1. AVL Trees (Authenticated Dynamic Dictionaries)#

  • Purpose: AVL Trees in Ergo are a specialized type of self-balancing binary search tree, used to store and authenticate dynamic sets of data in a compact and efficient manner. They ensure efficient and secure access to your data, guaranteeing optimal performance and data integrity.
  • Usage:
    • In the storage of UTXO states, where efficient verification of state changes is required.
    • In applications like off-chain code and distributed systems managing the Plasma infrastructure, where privacy-preserving transactions need to verify inclusion or exclusion of certain elements without revealing all details.
  • Documentation Reference: AVL Trees in Ergo, Plasma

2. Merkle Trees#

  • Purpose: Merkle Trees are a fundamental data structure in the Ergo blockchain, ensuring the integrity and authenticity of data. They play a crucial role in various blockchain operations, from verifying transactions within blocks to securing additional metadata in the Extension Block.
  • Usage:
    • In the construction of the Transaction Merkle Tree, combining all transactions and their corresponding spending proofs into a single Merkle Tree.
    • In the Extension Block Merkle Tree, securing key-value data like miner votes and protocol parameters.
    • In creating Merkle Batch Proofs, allowing efficient validation of the integrity and authenticity of data transactions. It supports the serialization and deserialization of Merkle proofs in batches, significantly improving the speed and efficiency of data verification processes.
    • In generating compact proofs of state transitions, enabling lightweight clients to securely participate in the network. An example of how a lite client can check a Merkle-tree-based membership proof is detailed in the Lite Client Checking Merkle Proof documentation.
  • Documentation Reference: Merkle Trees in Ergo

3. Sigma Trees (ErgoTree)#

  • Purpose: Sigma Trees, also known as ErgoTrees, are specialized data structures that represent logical propositions and cryptographic conditions in the Ergo blockchain. These trees are used in the execution of smart contracts and scripts, encapsulating complex logic and cryptographic proofs.
  • Usage:
    • In representing the logic and conditions of ErgoScript smart contracts.
    • In evaluating conditions for spending boxes (UTXOs) by verifying the cryptographic proofs and logic encoded in the ErgoTree.
    • Potential future integration with Merkle Trees (MT) or Sparse Merkle Trees (SMT) to enable working with Ergo transactions and the extension block database directly from ErgoScript.
  • Documentation Reference: ErgoTree

4. Context Data Structures#

  • Purpose: These structures represent the contextual information that is available during the execution of ErgoScripts. Contexts include details such as the current block height, the transaction being processed, and any additional data inputs.
  • Usage:
    • In providing necessary environmental details for smart contract execution.
    • In enabling the contextual flexibility of ErgoScripts.
  • Documentation Reference: Context Data Structures

5. Proof of Proof-of-Work (PoPow) Data Structures#

  • Purpose: These are specialized data structures used to implement PoPow, which allows lightweight nodes to verify the longest chain without downloading the entire blockchain.
  • Usage:
    • In creating and verifying interlink vectors, which are crucial for PoPow security.
    • In enabling lightweight clients to participate in the network with minimal data requirements.
  • Documentation Reference: PoPow Data Structures

6. Box Data Structures#

  • Purpose: Boxes are the fundamental data structures representing UTXOs in Ergo. Each box contains value, associated tokens, and an ErgoScript that defines spending conditions.
  • Usage:
    • In the creation and management of UTXOs.
    • In defining conditions for transaction execution within the blockchain.
  • Documentation Reference: Box Format

7. Transaction Data Structures#

  • Purpose: These structures represent the transactions within the Ergo blockchain. They include inputs, outputs, data inputs, and other necessary information for executing transactions.
  • Usage:
    • In organizing and executing financial transfers, contract calls, and state changes.
    • In ensuring the integrity and validity of transactions through the blockchain.
  • Documentation Reference: Transaction Format
  • Purpose: Used in conjunction with Merkle Trees for PoPow proofs, interlink vectors allow efficient verification of the chain of blocks in the blockchain.
  • Usage:
    • In the implementation of PoPow protocols for verifying blockchain headers.
  • Documentation Reference: Interlink Vectors

Potential Additional Data Structures#

As the Ergo ecosystem continues to evolve, additional data structures may be introduced, particularly in areas such as privacy-preserving protocols, advanced smart contract functionalities, or optimization of blockchain operations.

Hash-Based Accumulators#

For UTXO-based systems, simpler and well-studied hash-based accumulators are effective. Sparse Merkle Trees are sufficient for UTXO settings, though not the most efficient solution. More efficient alternatives include UTREEXO or the approaches described in this paper.

UTREEXO#

UTREEXO is a more efficient alternative for representing the UTXO set compared to traditional Merkle Trees. It allows for partially stateless clients, which can be practical in many scenarios. However, fully stateless clients still require archival nodes to store and update client proofs.

Partially Stateless Clients#

Ergo currently employs an approach outlined in this paper to support partially stateless clients. This approach balances security and efficiency, as fully stateless clients still depend on archival nodes for storing and updating client proofs.

Resources#

Comparison of AVL Trees and Merkle Trees in Ergo#

In Ergo, both AVL trees and Merkle trees play critical roles in ensuring the integrity, security, and efficiency of the blockchain. While they are both binary trees, their specific structures, purposes, and use cases differ significantly, making each suitable for different aspects of the Ergo ecosystem.

AVL Trees (Authenticated Dynamic Dictionaries)#

Overview: AVL trees in Ergo, particularly the AVL+ variant, are self-balancing binary search trees used to store and authenticate dynamic data sets. The main characteristic of AVL trees is their ability to maintain balance, which ensures that the height of the tree remains logarithmic in relation to the number of nodes. This property guarantees that operations such as search, insertion, and deletion can be performed efficiently, even as the data set grows.

Use Case in Ergo:

  • UTXO Set Management: AVL+ trees are employed to manage the UTXO (Unspent Transaction Output) set in the Ergo blockchain. Since UTXOs are frequently created and spent, the dynamic nature of AVL trees makes them ideal for this application. They support efficient updates while providing compact proofs for verification, which is crucial for maintaining the blockchain's performance.

Key Advantages:

  • Efficient Handling of Dynamic Data: AVL trees are optimized for scenarios where data changes frequently, such as the UTXO set, where coins are constantly being spent and created.
  • Compact Proofs: AVL+ trees generate compact proofs for the inclusion or exclusion of elements, aiding in efficient state verification.

Merkle Trees#

Overview:

Merkle trees are hash-based binary trees where each node contains a cryptographic hash. They are primarily used to ensure the integrity and authenticity of data. In a Merkle tree, leaf nodes represent individual data elements, and each non-leaf node is a hash of its child nodes. The Merkle root, derived from the tree, serves as a cryptographic commitment to the entire data set, allowing for efficient verification of data integrity through Merkle proofs.

Use Case in Ergo:

  • Transaction Verification: Merkle trees are used in Ergo to commit all transactions in a block into a single tree structure. The resulting Merkle root is included in the block header, enabling the network to verify the inclusion of any transaction within the block quickly.
  • Extension Block Security: Merkle trees are also utilized in the Extension Block to secure additional metadata, such as miner votes and protocol parameters. This ensures that the data has not been tampered with after the block is created.

Key Advantages:

  • Efficient Verification of Static Data: Merkle trees are particularly well-suited for static or infrequently changing datasets. They allow for quick verification of data integrity without the need to access the entire data set.
  • Compact Proofs: Merkle proofs are compact and efficient, making them ideal for verifying individual elements within a large dataset, such as transactions within a block.

Why Use AVL Trees or Merkle Trees?#

When to Use AVL Trees:

  • Dynamic Data Management: AVL trees are the preferred choice for dynamic data sets that require frequent updates, such as the UTXO set in Ergo.
  • Real-Time Applications: Their ability to maintain balance and support efficient insertions and deletions makes AVL trees ideal for real-time blockchain applications.

When to Use Merkle Trees:

  • Data Integrity and Authentication: Merkle trees excel in scenarios where data integrity needs to be proven without frequent modifications. They are perfect for static datasets where the structure remains relatively unchanged, such as in block headers or extension blocks.
  • Efficient Data Verification: For use cases requiring efficient verification of specific data elements within a large dataset, Merkle trees provide the necessary cryptographic proofs with minimal overhead.

Conclusion#

Both AVL and Merkle trees are indispensable in the Ergo blockchain, each serving distinct but complementary purposes. AVL trees are optimized for dynamic data management and are essential for handling the UTXO set, where data changes frequently. In contrast, Merkle trees are used to ensure the integrity and authenticity of static datasets, such as transactions within a block or data in the Extension Block, through efficient cryptographic proofs. Understanding these differences is crucial for developers working within the Ergo ecosystem to leverage the right data structure for their specific use case.